The present invention relates to a zero insertion force (ZIF) socket, and especially to a ZIF socket which ensures stable reliable electrical connection between an IC package and a circuit board without the help of a cam lever.
A conventional ZIF socket are disclosed in U.S. Pat. Nos. 5,489,218, and 5,679,020. Such conventional ZIF socket commonly has a cam attached between a base and a slidable cover for driving the slidable cover to slide along a top surface of the base from an original position to a final position. In the original position, pins of an IC package do not contact with the corresponding terminals fixed in the base. When the cover is driven by the cam to the final position, the pins of the IC package are properly positioned to electrically contact the corresponding terminals of the ZIF socket, and the cover is secured with the base at the final position. The cam is usually fixed to a lateral side of the ZIF socket, thus, the cam occupies a relatively large space and does not promote miniaturization of the ZIF socket.
A conventional ZIF socket without a cam is disclosed in U.S. Pat. No. 5,730,615. The ZIF socket comprises a base and a cover. Two expansion sections laterally extend from the base and the cover, respectively. Each expansion section defines a receiving slot therein whereby the cover is actuated to move in a front-to-end direction by inserting a flat tool into the receiving slots of both the base and the cover, and successively moving the flat tool in the receiving slots rearwardly and forwardly, whereby terminals fixed in the base electrical contact with corresponding pins of an IC package, which are positioned within the cover.
However, the conventional ZIF socket without a cam does not include a retention member to lock a cover of the ZIF socket at a final position the pins of an IC package engage with corresponding contacts of the ZIF socket. Therefore, the slidable covers are apt to move whereby the pins of the IC package may disengage from the contacts of the ZIF sockets when an exterior force is exerted on the ZIF socket.
Another conventional ZIF socket without a cam lever is disclosed in U.S. Pat. No. 4,988,310. The socket includes a base housing and a cover slidably mounted on the housing which drives pins of an IC package to electrically engage with corresponding contact elements disposed in the base housing. The socket further comprises a spring fixed in a slot defined in a lateral side of the base with legs extending into a corresponding slot defined in the cover. When the cover is moved by an external tool, the spring is biased to allow the pins of an IC package to engage with the contact elements of the socket. Since the inserting force exerted on the pins of the IC package by all the contacts is much greater than the biasing force exerted by the spring, the cover can not disengage from the pins without assistance from an external force provided by the socket.
The biasing force exerted by the spring can be balanced by some of the force exerted on the pins of the IC package by the contacts. However, the biasing force reduces a normal force exerted on the pins by the contacts thereby increasing contact impedance between the pins and the corresponding contacts. Thus, poor electrical connection quality will result.